Hemimegalencephaly: A Longitudinal MR Study Samuel M. Wolpert, Alan Cohen, and Mark H. Libenson Summary: An infant with hemimegalencephaly was studied with Seizures persisted, occurring many times daily. Two clin­ MR at 5 days and again at 10 months of age. The initial scan ical seizure types were recognized: one consisted of forced showed an abnormally large left cerebral hemisphere. At the age eye deviation to the right associated with clonic move­ of 10 months, the left cerebral hemisphere was smaller than the ments of the right side, and the other consisted of blinking, right-an apparent left-sided micrencephaly caused by normal facial twisting, and clonic movement of all limbs. growth of the right hemisphere and arrested growth of the left. Initial neurologic examination showed mild doli ­ The age of imaging of a patient with hemimegalencephaly can be chocephaly with a head circumference in the 50th to 75th important if the correct diagnosis is to be made. percentile and mild axial hypotonia. MR images obtained when the patient was 5 days old demonstrated an abnor­ Index terms: Megalencephaly; Brain, abnormalities and anoma­ mally large left cerebral hemisphere with pachygyria, lies; Brain, magnetic resonance; Pediatric neuroradiology thickened cortex, and periventricular cortical heterotopias (Fig 1 ). A diagnosis of left unilateral megalencephaly was Hemimegalencephaly, or unilateral megalen­ made. cephaly, is a rare anomaly of neuronal migra­ Electroencephalography demonstrated virtually contin­ tion and proliferation that usually presents with uous electrographic seizure activity referable to the left macrocephaly, intractable seizures, and devel­ hemisphere. Seizures remained refractory to multiagent opment of later contralateral hemiparesis and pharmacotherapy that included phenobarbital, phenytoin, mental retardation. Although usually unassoci­ valproic acid, and carbamazepine. The patient remained ated with other conditions, it has been described severely developmentally delayed. Head control was poor, in association with the linear sebaceous nevus and a left gaze preference and right homonymous hemi­ syndrome (1), the Klippel-Trenaunay-Weber anopsia were evident. A dense right hemiparesis devel­ syndrome (2), neurofibromatosis (3), and the oped with fisting of the right hand. MR images were re­ epidermal nevus syndrome (4). Somatic hemi­ peated when the patient was 10 months old (Fig 2). These hypertrophy generally is absent in the isolated demonstrated apparent asymmetric growth of the brain: form of the disease (5-13) but may occur in the previously described enlarged left cerebral hemisphere some patients (14, 15). There are autopsy (6), was now smaller than the right cerebral hemisphere, with evidence of central and peripheral atrophy of the left ce­ computed tomography (CT) (8), and magnetic rebral hemisphere. resonance (MR) (5) reports of the anomaly. In A left hemispherectomy was performed when the pa­ this paper, we report on an infant studied with tient was 1 0 months old. Intraoperative electrocorticogra­ MR at the age of 5 days and again at 10 months. phy demonstrated continuous multifocal seizure activity During this period, striking changes in the ap­ occurring over the left hemisphere convexity. The left pearance of the brain occurred. hemisphere appeared bosselated, and pathologic exami­ nation revealed polymicrogyria with gray matter heteroto­ pias. A calcarine cortex could not be identified. The sylvian Case Report fissure was abnormall y wide and the ventricle extreme ly The patient was the product of an uncomplicated preg­ large. nancy and presented with prolonged seizure activity on the The patient's seizures resolved after hemispherectomy, first day of life. He was born via spontaneous vaginal and he demonstrated dramatic neurologic improvement. delivery at 7 pounds 4 ounces to a healthy 26-year-old Two months after surgery a ventricular shunt was inserted mother. There was no family history of neurologic disease. to control hydrocephalus. At follow-up examination at 23 Seizures first developed when the patient was 2 hours old. months of age, he had remained seizure-free since the Received September 21 , 1992; accepted after rev ision February 22, 1993. From the Section of Neuroradiology (S.M.W.), Depa rtment of Neurosurgery (A.C.) , and Division of Pediatric Neurology (M.H.L.) , New England Med ical Center Hospitals, Boston. Address reprint requests to Samuel M. Wolpert, MD, 750 Washington St. Boston, MA 02111. AJNR 15:1 479-1482, Sep 1994 0195-6108/94/1508-1 479 © American Society of Neu roradiology 1479 1480 WOLPERT AJNR: 15, September 1994 Fig 1. A and B, 5 days of age. A xial T l -weighted MR image, 650/20/ 1 (repeti­ tion time/echo time/excitations) through central white m atter dem onstrates enlarged abnormal left hemisphere with thic k gray m atter and pachygyria ( w hite arrows) and hyperintense white matter (blac/c arrows). B is 8 mm, higher than A . Note also en­ larg ed left lateral ventricle. (Right lateral ventricle, not shown here, was seen on lower sections.) C and 0 , A xial T2-weighted images, 3000/1 40/1 , at sa m e levels as A and B dem onstrates thick pachygyri c gray m atter (open arrows), enlarg ed left lateral ventri­ cle, and minimal hyperintensity of sur­ rounding white m atter (arrows) caused pre­ sumably by gliosis. D immediate postoperative peri od, was able to sit if placed, swelling is usually present (17). In unilateral used three words specifi call y, and demonstrated a mild megalencephaly (hemimegalencephaly), the right hemiparesis and a left gaze preference. The electro­ white matter is usually excessive, and the nerve encephalogra m showed a normal posterior rh ythm on the right a nd voltage depression on the left ; there was no cells are larger and less densely packed than on residual epile ptiform activity. the normal half of the brain ( 6), and polymicro­ gyria, neuronal heterotopias (11), and lissen­ cephaly occur. Unilateral megalencephaly is Discussion probably related to an interference in normal Unilateral megalencephaly is considerably neuronal migration along radially oriented glial less common than the generalized fo rm , which fibers (18, 19). Gliosis and/or heterotopic gray has been divided into anatomic megalen­ matter may occur in the white matter (5). cephaly (including the neurocutaneous syn­ Brain growth after birth is largely determined dromes and a variety of genetic syndromes) by glial rather than by neuronal growth (20). In and metabolic megalencephaly (1 6). In this lat­ an infant with hemimegalencephaly, it is ex­ ter group of disorders, which includes Tay­ pected that through childhood the normal hemi­ Sachs disease and other gangliosidoses , Cana­ sphere should undergo normal growth, matura­ van disease, Alexander disease, and some of tion, and myelination. The MR appearances in the mucopolysaccharidoses, white matter this case report are consistent with normal neu- AJNR: 15, September 1994 HEMIMEGALENCEPHALY 1481 Fig 2. A and B, 10 m onths of age. Axial T1-weighted MR image 650/20/1 at ap­ proximately the same levels as Figure 1 A and B dem onstrate a sm aller left than right hemisphere. Again left-sided pachygyria is seen (arrows) . The subarachnoid spaces surrounding the hemisphere are wider on the left than on the right side. Note that the left hemicranium remains larger than the right des pite the atrophic underl ying hemisphere. C and 0 , Axial T2-weighted images, 3000/ 140/1 at the same levels as A and B demonstrate again a smaller left than right hemisphere. Again left-sided pachygyria is noted. There are hyperintense areas (arrows) surrounding the left occipital horn because of gliosis. D ronal and glial proliferation in the "normal" with hemimegalencephaly. The child did not hemisphere. It is not clear what later effect the in experience any clinical event during his course utero event that lead to the subsequent malde­ that would account for the failure of the affected velopment and abnormal prenatal enlargement hemisphere to grow. One could speculate that of the left hemisphere (likely occurring in the the patient's poorly controlled seizures were re­ second trimester of pregnancy) should have on sponsible for some portion of the growth arrest later brain growth. It would not be unexpected of the involved hemisphere, but the extent of the that such a severely disorganized region of ce­ growth differential makes seizures as the sole rebrum would have limited future growth poten­ explanation for the discrepancy implausible. tial. A review of the literature, either through longitudinal studies or in studies of patients di­ References agnosed in the first years of life, however, fails to demonstrate this consequence of differential 1. Hag er BC , Dyme lZ, Guertin SR, Tyler RJ, Tryciecky EW, Fratkin brain growth in patients with hemimegalen­ JD. Linear nevus seba ceous sy ndrome: megalenceph aly and het­ erotopic gray matter. Ped iatr f'leuro/1991 ;7:45-49 cephaly. We cannot account for the lack of sim­ 2. Burke JP, West NF, Strachan IM. Congenital nysta gmus, ani ­ ilar descriptions in the literature of differential somyopia , and hemimega lence phaly in the Klippei-Trenaunay­ growth of the cerebral hemispheres in patients Weber syndrome. J Pediatr Ophthal Strabis 1991 ;28:41 - 44 1482 WOLPERT AJNR: 15, September 1994 3. Cusmai R, Curatolo P, Mangano S, Cheminal R, Echenne B. Hemi­ 12. Tijiam AT, Stefanko S, Schenk VWD, de Vlieger M. Infantile megalencephaly and neurofibromatosis. Neuropediatrics 1990; spasm associated with hemihypsarrhythmia and hemimegalen­ 21 :179-182 cephaly. Deu fvled Child Neurol1978;20:779-798 4. Pavone L, Curatolo P, Rizzo R, et al. Epidermal nevus syndrom e: 13. Townsend JJ, Nielsen SL, Malamud N. Unilateral m ega len­ a neurologic variant with hemimegalencephaly, gyral malforma­ cephaly: hamartoma or neoplasm? Neurology 1975;25:448-453 tion, mental retardation, seizures, and facial hemihypertrophy. 14. Hallervorden J . Microscopic findings in brain in case of congenital Neurology 1991 ;41(Part 1):266-271 hemihypertrophy of left side of body including brain.